1. Field of the Invention
The present invention relates to the field of solar energy recovery systems.
2. Prior Art
Considerable engineering effort has been directed for many years toward the practical and efficient recovery of solar energy. Panels and systems for the recovery of solar energy in the form of both a heat source and in the form of electrical power are known, though in general such systems have not found general application probably because of their cost and the relatively low cost of electrical power and gaseous and liquid hydrocarbon fuels until very recent times. The cost of solar energy recovery systems has probably been one of the determining factors limiting the general application thereof, and is expected to continue to be an important factor as building costs are generally considered to be very high and few persons will tolerate an increase therein unless absolutely necessary. Thus to achieve general acceptance and application, the cost of the solar energy recovery system should be kept as low as possible. As shall subsequently be seen the present invention utilizes recovery panels not only serving as solar energy collectors but futher serving as decorative roofing panels providing a waterproof covering for the corresponding area of a building roof, so as to provide the dual function of energy collection and roofing in a simple and decorative manner. Further, the roofing panels are generally very light, even when simulating heavier materials such as tile, so that oftentimes the desired aesthetic character of the building may readily be achieved while effecting structural savings in the building itself because of the grossly reduced roof loading.
Since the present invention is particularly directed to the recovery of solar energy at least initially in the form of heat, only the prior art panels adapted for a similar purpose shall be described herein. The most common such solar panel presently in use for space heating, space cooling and domestic hot water heating is the liquid cooled doubled glazed flat plate collector. Such collectors generally operate on the greenhouse principle, that is, they receive light generally in the visible spectrum, convert the light to longer wavelength energy and then resist the reradiation of the converted energy, thereby allowing the accumulation and recovery of the energy in the form of heat. Thus a transparent panel such as a glass panel is desired for the outer facing panel, characterized by a high transmission of visible energy and the relatively low transmission of longer wavelength energy. While structurally, and from a cost standpoint, some plastics would be desirable for such use, most plastics do not have the desired optical characteristics, and accordingly represent poor choices for the stated purpose. However at least the structure of such panels is relatively simple in concept, and can be fabricated by almost any handyman to have an acceptable performance over a wide range of temperatures.
A preferred construction for such panels, from the standpoint of efficiency, may include copper waterways, aluminum fins, tempered glass or Tedlar glazing, aluminum or galvanized steel housings with appropriate insulation, and selected coatings, thereby resulting in both relatively high cost and substantial weight for the energy collection panels. In addition, the appearance of such flat plate collectors is anything but decorative. The characteristic smooth, shiny glazed surfaces of the panels do not create any visual interest, and are not complementary to most architectural styles. Therefore in most installations to date the panels are placed on flat roofs hidden from view from street level by shallow peripheral walls, perhaps set off aesthetically with mansards and the like.
Another deficiency of flat plate collectors is their lack of durability. Glass glazing typically weathers well but is vulnerable to vandalism, hail damage and the like. Tedlar is probably more resistant to hail and vandalism than glass but is very vulnerable to wind damage if not kept taut at all times. Further, while a rock or branch may not puncture a Tedlar film, it may cause local stretching and deforming so that subsequent winds can flap the loose film in this area causing premature fatigue failures.
Lucite and plexiglass sheets with suitable ultraviolet inhibitors are also used as glazing materials. These materials are resistant to mechanical and wind damage, though they have the disadvantage of being relatively transparent to long wavelength radiation. While this transparency can be at least partially offset by providing selective coatings on the copper waterways and their fins, such selective coatings, as previously mentioned, are themselves relatively expensive. Further, any form of plastic covering is generally subject to scratching, thereby increasing maintenance costs by requiring more care when cleaning their surfaces.